As a third wave of world information industry development following computers and the Internet, the Internet of Things will change various aspects of humans, such as life, work, and production. The Internet of Things has rich connotations. The Internet of Vehicles, a smart household, a smart city, and the like that have recently drawn wide attention in the academic and industrial circles are all specific implementation forms of the Internet of Things. To implement the Internet of Things, a huge quantity of interconnected machine-type devices (machine-type devices) such as sensors and radio frequency identification tags need to be deployed. A cellular network is a simplest and most practical network architecture that can implement the Internet of Things.
To implement the Internet of Things or a wireless ad hoc network in the cellular network, cell densification will become a trend of a future network, and massive access (Massive Access) will become one of typical scenarios of the future network.
Characteristics of the massive access lie in:
Firstly, a quantity of potential access terminals is relatively large and dynamically changes.
Secondly, an access network structure is complex, a topology is variable, and a channel characteristic dynamically changes.
Thirdly, service types are complex; there may be distinct differences in data amounts for access of different terminals, possibly ranging from several bits to a large amount of data; and some real-time control networks have a relatively high requirement on a delay.
Characteristics of a scenario assumed for a conventional multiple access mechanism are: A quantity of terminals is small, but a data amount of each terminal is relatively large. These are obviously different from the characteristics of the massive access scenario. If the conventional multiple access mechanism is used for massive access, problems such as low efficiency, high signaling overheads, and high complexity are caused.
Based on this, in a current non-orthogonal access mechanism of sparse code multiple access (sparse code multiple access, SCMA), each signature in a low-density signature matrix is corresponding to L pilots, and a process of contention-based access is: A terminal first sends a pilot, where the pilot is randomly selected by the terminal, and then maps, by using a signature (Signature) corresponding to the pilot, data to a multi-dimensional symbol for data sending; and a base station first detects a pilot, and if a specific pilot is detected, this is equivalent to that a signature is detected, and the base station decodes received data according to the signature. In the current SCMA access mechanism, when different terminals happen to choose different pilots of a same signature, the base station can learn that the different terminals send data by using the same signature, and in this case, the base station can restore data by means of channel estimation of each terminal; or when different terminals choose a same pilot of a signature, due to a pilot conflict, the terminals execute a random backoff process to retransmit data.